Coupling of butyl vinyl tellurides with metal acetylides catalyzed by nickel complexes

Article abstract of DOI:10.1016/j.tetlet.2004.04.120

Z-Vinylic tellurides react with metal acetylides under nickel complexes catalysis to give Z-enynes and Z-enediynes in good yields.

Full text of DOI:10.1016/j.tetlet.2004.04.120

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 4927–4930
Coupling of butyl vinyl tellurides with metal acetylides catalyzed by
nickel complexes
a
Cristiano Raminelli, Joao Gargalaka, Jr., Claudio C. Silveira and Joao V. Comasseto
a
b
a,
*
~
ꢀ
~
aInstituto de Quꢀımica, Universidade de S~ao Paulo, Av. Prof. Lineu Prestes, 748 – Cx.P. 26077, 05599-970 S~ao Paulo, Brazil
bDepartamento de Quꢀımica, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS, Brazil
Received 12 November 2003; accepted 21 April 2004
Available online 10 May 2004
Abstract—Z-Vinylic tellurides react with metal acetylides under nickel complexes catalysis to give Z-enynes and Z-enediynes in good
yields.
Ó 2004 Elsevier Ltd. All rights reserved.
The transformation of Z-vinylic tellurides into reactive
Z-vinylic organometallics is nowadays well established1
and found use in the total synthesis of Macrolactin A, a
polyunsaturated macrocyclic lactone with anti-viral
activity.2 Recently we turned our attention to the direct
transformation of Z-vinylic tellurides into Z-enynes and
Z-enediynes through the palladium promoted coupling
of Z-vinylic tellurides with alkynes.3 This reaction
experienced a rapid growth and found use in the con-
struction of a number of unsaturated systems.4 In view
of the high coast of the palladium reagents, we are in
the search for less expensive methods to promote the
alkyne–telluride coupling. An alternative should be
the use of nickel catalysts5 and recently one of us
found that Ni(dppe)Cl2 3 in the presence of CuI
promotes the coupling of bis-vinylic tellurides 1 with
alkynes 2 (Scheme 1), leading to enynes 4a in good
yields.6
However, the preparation of bis-vinylic tellurides by
hydrotelluration of alkynes is not general, specially for
the preparation of telluroenynes 5. Attempts to prepare
5 by this method led to the formation of tellurophenes 6,
as described earlier.7 The hydrotelluration leading to
butyltelluroenynes 7, on the contrary, is quite general
producing the desired Z-vinylic tellurides in good yields1
(Scheme 2).
In view of this we attempted the coupling of Z-butyl
vinyl telluride 8a with 1-heptyne using the conditions
shown in the Scheme 1.6 To our surprise the coupling
did not occur. Then, instead of an alkyne we used an
alkynoate 9, this time using Ni(PPh3)2Cl2 as the catalyst
in the absence of CuI (Scheme 3).
The reaction occurred in good yields giving the enyne 4a
with retention of the Z stereochemistry. As can be
Ph
Te
1
+
Ph
Ni(dppe)Cl2 (5 mol %)
Ph
3
CuI (5 mol %), Pyrrolidine,
Ar, r.t., 20 h
4a
78%
2
H
Scheme 1.
Keywords: Z-Butyl vinyl tellurides; Nickel complexes catalysis; Coupling reaction.
* Corresponding author. Tel.: +55-11-30912176; fax: +55-11-38155579; e-mail: jvcomass@iq.usp.br
0040-4039/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.04.120

4928
C. Raminelli et al. / Tetrahedron Letters 45 (2004) 4927–4930
sponding magnesium alkynoate 9a. By changing
R
R
Ni(PPh3)2Cl2 for Ni(dppe)Cl2 (3) a substantial increase in
the yield was observed (Table 1, entry 1). In view of this
fact we adopted the use of Ni(dppe)Cl2 (3) (5 mol %) and
the lithium alkynoate (9b) (2.5 equiv) to perform a sys-
tematic study of the coupling reaction. The yields of the
coupled products were high in most cases (Table 1,
Eq. 1).8
Te
M2Te
5
R
R
(n-BuTe)2,
R
R
NaBH4, EtOH
Te
R
6
As can be observed in Table 1, the vinylic telluride 8e
with a OTBS group at C3 did not give the coupling
reaction (entries 8 and 9), suggesting some steric influ-
ence of the bulky group at C3 of the vinylic telluride.
The vinylic telluride 8d coupled efficiently with the
lithium alkynoate and the protecting group was
removed during the reaction leading to the alcohol 4g in
quantitative yield. Attempts to reduce the amount of the
lithium alkynoate (9b) from 2.5 to 1.5 equiv using 8a and
Ni(dppe)Cl2 (3) (5 mol %) was satisfactory, however, the
TeBu
7
R
Scheme 2.
observed in Scheme 3, reaction with the lithium alkynoate
9b gave higher yield than the reaction with the corre-
Ph
Ni(PPh3)2Cl2 (5 mol%)
(2.5 equivalents)
Ph
TeBu
8a
9
M
4a
THF, N2, reflux
M = MgBr (9a) 70% (4h)
Li (9b) 90% (3h)
Scheme 3.
Table 1.
R
Ni(dppe)Cl2 (5 mol%)
3
R
TeBu
ð1Þ
4
R'
Li
8
R1
(2.5 equivalents)
THF, N2, reflux
Entry
1
R
R1
Product
Reaction time (h)
3
Yield (%)a;b
100
Ph
n-C5H11
4a
4b
8a
2
Ph
Ph
12
93
8a
O
N
O
N
N
3
4
n-C5H11
7
4
100
64
4c
8b
O
N
O
Me3Si
Si
4d
8b
5
6
n-C5H11
5
5
97
75
4e
8c
8c
4f

C. Raminelli et al. / Tetrahedron Letters 45 (2004) 4927–4930
4929
Table 1 (continued)
Entry
R
R1
Product
Reaction time (h)
12
Yield (%)a;b
100
HO
7
8
9
n-C5H11
TMSO
4g
8d
TBSO
n-C5H11
12
12
Nrc
Nrc
OTBS
4h
8e
TMSO
Ph
OTBS
4i
8e
a Isolated yield after column chromatography in silica gel.
b The analytical data agree with the structures proposed.
c The product was not formed.
OH
3, THF, N2, reflux 3 h
Li
EtO
TeBu
)
2
O
8f
9b
10
ZnCl2
O
ZnCl
9c
3, THF, N2, reflux 3 h
O
78%
(E:Z / 95:5)
4j
Scheme 4.
yield dropped to 87%. Use of 1.5 equiv of 9b and
1 mol % of Ni(dppe)Cl2 gave only trace amounts of the
product 4a after 24 h. By performing the reaction at
room temperature the product 4a was obtained also in
trace amounts after 72 h.
values for trans-olefins. A low intensity doublet at
6.01 ppm with coupling constant of 11.4 Hz indicate the
presence of the Z isomer. The 95:5 ratio was confirmed
by a GC analysis.
In conclusion, the results reported in this communica-
tion show that the coupling of Z-vinylic tellurides with
metal alkynoates under nickel complexes catalysis is a
convenient method to synthesize enynes and enediynes,
being less expensive than our previous method,3 which
make use of palladium chloride.
The functionalized vinylic telluride 8f on reaction with
the lithium alkynoate 9b gave the coupling product,
however, besides the coupling reaction, the addition of
the alkynoate to the ester group also occurred, leading
to 10 (Scheme 4). To avoid this undesired side reaction
the more selective zinc alkynoate 9c, prepared by a
transmetallation reaction between the lithium alkynoate
9b and ZnCl2, was used. Reaction of 9c with 8f under
the coupling conditions gave the functionalized enyne 4j
in 78% yield.9 However, under the reaction conditions
used, the configuration of the Z-vinylic telluride 8f was
not maintained and 4j was obtained as a diastereomeric
mixture of E and Z olefins in a 95:5 ratio (Scheme 4).
Probably the long heating of the reaction mixture pro-
motes the isomerization of the conjugated system pres-
ent in 4j. The stereoisomeric ratio was determined by
analysis of the 1H NMR spectrum. The E-vinylic
hydrogens resonate as a double triplet at 6.75 ppm with
coupling constants of 15.8 and 2.2 Hz and as a doublet
at 6.13 ppm with a coupling constant of 15.8 Hz, typical
Acknowledgements
The authors acknowledge the following agencies for
support: CNPq and FAPESP.
References and notes
1. For leading references see: (a) Barros, S. M.; Comasseto,
J. V.; Berriel, J. N. Tetrahedron Lett. 1989, 30, 7353;
(b) Tucci, F. C.; Chieffi, A.; Comasseto, J. V. Tetrahe-
dron Lett. 1992, 33, 5721; (c) Tucci, F. C.; Chieffi, A.;

4930
C. Raminelli et al. / Tetrahedron Letters 45 (2004) 4927–4930
Comasseto, J. V.; Marino, J. P. J. Org. Chem. 1996, 4975;
2863, 2200, 1494, 1455, 1422, 783, 692; LRMS m=z (relative
intensity) 198 (Mþ, 36.8%), 183 (5.2%), 169 (10.4%), 155
(23.3%), 141 (100.0%), 128 (42.9%), 115 (66.3%), 102
(4.8%), 91 (33.6%), 79 (14.5%), 63 (12.3%), 55 (11.0%), 51
(10.2%), 41 (16.3%).
For recent reviews see: (d) Comasseto, J. V.; Barrientos-
Astigarraga, R. E. Aldrichim. Acta 2000, 33, 66; (e) Vieira,
M. L.; Zinn, F. K.; Comasseto, J. V. J. Braz. Chem. Soc.
2001, 12, 586.
2. Marino, J. P.; McClure, M. S.; Holub, D. P.; Comasseto, J.
V.; Tucci, F. C. J. Am. Chem. Soc. 2002, 124, 1664.
3. Zeni, G.; Comasseto, J. V. Tetrahedron Lett. 1999, 40, 4619.
4. For a review see: Zeni, G.; Braga, A. L.; Stefani, H. A. Acc.
Chem. Res. 2003, 36, 731.
5. Komiya, S. In Synthesis of Organometallic Compounds––A
Practical Guide; Komiya, S., Ed.; John Wiley and Sons:
Chichester, 1997; Vol. 1, p 249.
6. Silveira, C. C.; Braga, A. L.; Vieira, A. S.; Zeni, G. J. Org.
Chem. 2003, 68, 662.
7. Renson, M. In The Chemistry of Organic Selenium and
Tellurium Compounds; Patai, S., Rappoport, Z., Eds.; John
Wiley and Sons: Chichester, 1986; Vol. 1, p 399.
8. Typical procedure for the preparation of lithium alkynoates:
preparation of 1-heptynyl lithium: To a 50 mL two-necked
round-bottomed flask under nitrogen atmosphere were
added THF (10 mL) and 1-heptyne (11 mmol, 1.10 g,
1.5 mL). Then n-BuLi (7.7 mL; 10 mmol of a 1.3 M solution
in hexane) was added dropwise at ꢀ70 °C. The mixture was
stirred for 10 min. After this time the solution of 1-heptynyl
lithium is ready for use.
9. Transmetallation reaction between 1-heptynyl lithium (9b)
and ZnCl2: preparation of 9c: To 1-heptynyl lithium
(14.4 mL; 7.5 mmol of a solution prepared as above) under
nitrogen atmosphere, at ꢀ70 °C was added ZnCl2 (7.5 mL;
7.5 mmol of a 1 M solution in THF). The mixture was stirred
at room temperature for 20 min. After this time the solution
of 9c is ready for use. Coupling reaction of 8f with 9c:
preparation of compound 4j: To a 100 mL two-necked round-
bottomed flask under nitrogen atmosphere were added
Ni(dppe)Cl2 (0.15 mmol, 0.079 g), THF (30 mL), the Z-
vinylic telluride 8f (3 mmol, 0.851 g) and then the zinc
alkynoate 9c (21.9 mL; 7.5 mmol of the solution prepared
above) via syringe. The mixture was refluxed for 3 h. The
reaction was quenched with brine (100 mL) followed by
extraction with ethyl acetate (3 ꢁ 100 mL). The extracts were
dried over MgSO4. The solvent was filtrated and evaporated
and the residue was first purified by flash chromatography
eluting with hexane and then with ethyl acetate. The residue
was further purified by horizontal distillation under reduced
pressure to give 0.455 g (78%) of 4j as a E/Z mixture in a 95:5
ratio. E stereoisomer: 200 MHz 1H NMR (CDCl3, ppm)
6.75 (dt, J ¼ 15:8, 2.2 Hz, 1H), 6.13 (d, J ¼ 15:8 Hz, 1H),
4.20 (q, J ¼ 7:0 Hz, 2H), 2.37 (td, J ¼ 7:0, 2.2 Hz, 2H), 1.56
(quint, J ¼ 7:0 Hz, 2H), 1.44–1.30 (m, 4H), 1.28 (t,
J ¼ 7:0 Hz, 3H), 0.91 (t, J ¼ 7:0 Hz, 3H); 50 MHz 13C
NMR (CDCl3, ppm) 165.90, 129.14, 125.92, 100.54, 77.84,
60.33, 30.90, 27.90, 22.00, 19.54, 14.02, 13.71; IR near (film)
(cmꢀ1) 3069, 2959, 2934, 2866, 2215, 1719, 1619, 1463, 1368,
1302, 1157, 963; LRMS m=z (relative intensity) 194 (Mþ,
3.6%), 179 (16.3%), 165 (40.9%), 149 (42.3%), 133 (20.0%),
119 (52.0%), 109 (44.9%), 93 (62.2%), 79 (100.0%), 65
(47.5%), 55 (76.5%), 41 (69.1%). The Z isomer was identified
in the mixture by its LRMS m=z (relative intensity) 194 (Mþ,
1.9%), 179 (0.7%), 166 (35.9%), 149 (22.2%), 137 (13.3%),
123 (47.0%), 109 (100.0%), 91 (20.6%), 81 (69.6%), 65
(28.8%), 55 (48.9%), 41 (49.4%) and by a low intensity
doublet at 6.01 ppm with a coupling constant of 11.4 Hz in
the 1H NMR spectrum. A GC analysis of the purified
product showed that it was constituted by a 95:5 mixture of
the E and Z isomers of 4j, respectively.
Typical procedure for the coupling reaction: preparation of
compound 4a: To a 25 mL two-necked round-bottomed
flask under nitrogen atmosphere were added Ni(dppe)Cl2
(0.05 mmol, 0.026 g), THF (10 mL), the Z-vinylic telluride
8a (1 mmol, 0.288 g) and then 1-heptynyl lithium (4.8 mL;
2.5 mmol of the solution prepared above) via syringe. The
mixture was refluxed for 3 h. Then the reaction was
quenched with brine (50 mL) followed by extraction with
ethyl acetate (3 ꢁ 50 mL). The extracts were dried over
MgSO4 and then filtered and evaporated. The residue was
purified by column chromatography on silica gel eluting
with hexane to give 4a in quantitative yield (0.198 g). 1H
NMR (300 MHz, CDCl3, ppm) 7.88–7.85 (m, 2H), 7.37–
7.24 (m, 3H), 6.55 (d, J ¼ 12:0 Hz, 1H), 5.70 (dt, J ¼ 12:0,
2.4 Hz, 1H), 2.43 (td, J ¼ 7:0, 2.4 Hz, 2H), 1.61 (quint,
J ¼ 7:0 Hz, 2H), 1.49–1.29 (m, 4H), 0.92 (t, J ¼ 7:0 Hz,
3H); 13C NMR (75 MHz, CDCl3, ppm) 137.21, 136.69,
128.43, 128.12, 128.09, 108.20, 97.88, 79.16, 31.16, 28.28,
22.25, 19.87, 13.99; IR near (film) (cmꢀ1) 3058, 3021, 2990,